Justification:
Listed as Critically Endangered because of a drastic population decline, estimated to be more than 80% over the last three generations, inferred from the apparent disappearance of most of the population; and because its Extent of Occurrence is less than 100 km2, and its Area of Occupancy is less than 10 km2, its distribution is severely fragmented, and there is continuing decline in the extent and quality of its habitat, area of occupancy, number of subpopulations, and number of mature individuals; and because its population size is estimated to number fewer than 250 mature individuals, with no sub-population greater than 50 individuals, and it is experiencing a continuing decline.

This species is restricted entirely to the Baw Baw Plateau, located approximately 120km east of Melbourne, Victoria (Malone 1985a; Hollis 1995). Despite searches in close proximity to the plateau, and in similar environments (e.g., Mount Useful, Mount Torongo), the species has not been found elsewhere. Encompassing an area of approximately 80km², the Baw Baw Plateau between approximately 1,260 and 1,560m asl is contained within the Baw Baw National Park, except for approximately 3.5km² near Mount Baw Baw that is managed by the Victorian Alpine Resorts Commission (Hollis 1997). At lower elevations, between 960 and 1,300m asl, records of the species occur from montane forest along the south escarpment of the Baw Baw Plateau (G. Hollis pers. comm.). In 1983 and 1984, Malone (1985a) undertook a comprehensive assessment of the distribution of the species. It was found to be widely distributed and abundant in the west (Mt Baw Baw), central (Mt St Phillack) and north-west (Mt Whitelaw) parts of the plateau. There were fewer records from the east region (Mt St Gwinear), and the species was conspicuously absent from the south-east region. The distribution map shows the historical and not current range of the species. It has now disappeared from over 80% of its former occupied range.

Malone (1985a) estimated the adult male population on the plateau to be over ten thousand individuals. During a series of extensive annual surveys carried out since 1993, a considerable reduction in the abundance of the species has been observed (Hollis 1995, 1997; Osborne, Hunter and Hollis 1999). Malone (1985a) recorded calling males in 73% (64 of 88) of frost hollows surveyed in 1983 and 1984, compared with 46% (22 of 48) recorded by Hollis (1995) in 1993. In a subset of 35 frost hollows surveyed in both 1983 and 1993, Malone (1985a) recorded 3,694 males compared with 83 by Hollis (1995). Similarly, in a subset of 19 frost hollows surveyed in both 1984 and 1993, 885 males were recorded in 1984 compared with 19 in 1993. Hollis (1995) and Osborne, Hunter and Hollis (1999) only recorded 2.2% and 2.1% of the number of males recorded by Malone in 1983 and 1984, respectively. Surveys during subsequent years (1994-1997) indicate that the species is currently restricted to the western half of the Baw Baw plateau (particularly to steeper montane-forested areas on the edge of the western plateau (W. Osborne pers. comm.), with a contraction of the distribution from eastern and western areas (Osborne, Hunter and Hollis 1999). Twenty-four sites surveyed on the Baw Baw plateau originally by Malone (1985a) were re-surveyed annually by Osborne, Hunter and Hollis (1999) for numbers of calling males present. At all sites, there was a very large reduction in the numbers recorded. The mean number of calling males recorded at 24 sites declined from 124 individuals in 1983 to between 1.5 and 3.3 individuals over the five years 1993 to 1997. In 1983-1984 the maximum population size recorded at a monitoring site was 667 individuals; by contrast, between 1993 and 1997 the largest population recorded was 41 individuals. In 1997 frogs were recorded at only six of the 25 monitoring sites. Overall, the current population size is estimated to be less than 250 adults, a tiny fraction of the number estimated only 20 years earlier by Malone (1985a).

This species is a habitat specialist. During the breeding season (September-December), calling males, gravid females and egg masses have been recorded, along seepage lines within or at the periphery of sub-alpine wet heathland and in gullies within montane vegetation communities (Malone 1985a; Hollis 1995). Calling activity has been recorded in early September, continuing as late as the last week in December (Malone 1985a; Hollis 1995; G.J. Hollis. pers. comm.). Oviposition (egg laying) appears to be confined to a shorter interval of 2-3 weeks during this period, when a peak in calling activity occurs (Malone 1985a, b; Hollis 1995). The timing of this peak in calling activity varies between breeding seasons (Hollis 1997). Calling activity may occur at any time of the day or night, with the greatest levels of activity being recorded during relatively warm, humid conditions (Hollis 1997). Very little calling activity occurs at temperatures near freezing (Malone 1985a) or when temperatures are high with low humidity (Hollis 1997). Egg masses are deposited in a transparent foam nest (8cm diameter and 3-4cm high) at the calling site, or nearby, during inguinal amplexus (Littlejohn 1963). The foam nest is produced by the female beating air bubbles into the mucous and eggs with flanged fingers during egg laying (Littlejohn 1963). The egg mass may be deposited at varying depths in vegetation, or below the ground surface, depending on the structural attributes of the site (Hollis 1997). Depths of over a metre have been observed, whilst others are deposited in vegetation very close to the surface (Hollis 1997). Clutch sizes reported in the literature range from 50-185 (see Littlejohn 1963; Malone 1985a, b; Tyler 1992). Ova are white and unpigmented and measure on average 4mm in diameter (Malone 1985b). Oviposition of more than one clutch may occur at a single site (Malone 1985b; Hollis 1997). It is also possible that females deposit a portion of their eggs at more than one site (Malone 1985a). Under natural conditions the embryonic period varies from 5-8 weeks, with individuals hatching at Gosner stages 22-23 (Malone 1985a, b). The larvae are non-feeding, hatching with a residual yolk mass that maintains them through to metamorphosis (Malone 1985a, b). Larvae usually remain at oviposition sites through to metamorphosis (Barker, Grigg and Tyler 1995; Hollis 1997). Upon hatching, however, larvae have also been observed to move small distances in shallow water from oviposition sites, while remaining covered under vegetation and/or woody debris (Hollis 1997), or to be washed into nearby pools (B.S. Malone pers. comm. in Hollis 1997).

The dearth of information available on the population dynamics and demography of the Baw Baw Frog makes it very difficult to interpret the observed decline in the adult male population. This decline coincides with a recent global phenomenon of declining amphibians (e.g., Barinaga 1990; Blaustein and Wake 1990; Tyler 1991), and perhaps of more concern, with the reported decline of species restricted to mountain-top and alpine environments in Australia (e.g., Osborne 1990; Richards, McDonald and Alford 1993) and overseas. Numerous hypotheses have been generated to explain these declines, but few as yet have been investigated thoroughly. Those that have, or are currently being investigated, include climate change (Osborne 1990; Richards, McDonald and Alford 1993), ultraviolet radiation (Blaustein et al. 1994), atmospheric pollution (Blaustein et al. 1994) and pathogens (such as chytridiomycosis) (Blaustein et al. 1994; Trenerry, Laurance and McDonald 1994), but there is growing scientific consensus that chytridiomycosis is often implicated. No thorough investigation of these hypotheses has yet been undertaken for the Baw Baw Frog. Forestry operations might also represent a threat to the species where it occurs in State Forest (W.S. Osborne pers. comm.). Willow (Salix cinerea), cattle, rabbits, Sambar deer, foxes, dogs and cats have been identified as invasive species that might be impacting the species (G.J. Hollis pers. comm.).

The species' habitat is protected within Baw Baw National Park, and the species is listed as endangered in Australian legislation. Research and monitoring are currently in place. The implementation of a focused recovery plan is clearly needed, and this will probably need to include an ex-situ component.